This invention relates to a spectrometer and, more particularly, to a miniature spectrometer for placement within a body for tissue characterization.
Spectral analysis of living tissue can be used to detect various forms of cancer and other types of diseases. In spectral analysis, light illuminates tissue region under examination and a light detector detects optical properties of the illuminated tissue region by measuring light energy modified by its interaction with the tissue region in a pre-determined frequency and amplitude domain. Optical properties include absorption, luminescence, fluorescence, frequency and time-domain responses to various materials injected to the tissue region and other electromagnetic responses. Diseased tissue may be identified by comparing a spectrum obtained to spectra of normal tissue obtained under the same controlled conditions.
Current devices available for tissue characterization using spectral analysis include night vision sensing systems with filtering adapted to be used with endoscopes and multichannel fiber optic delivery systems. The latter systems typically include a light source, an optical conduit, a light applicator and receiver, a second light conduit, a spectrometer and a display unit. These systems tend to be very expensive, to require large accompanying electronic systems, and to be complex requiring operator training.
The optical fibers used as optical conduits in the multichannel fiber optic delivery systems are source of design difficulties. In order to transport an adequate amount of light energy from the light source to a tissue region inside a body, a significant amount of optical fibers must be included in an interventional device. An interventional device, such as a catheter, however, does not include a lot of space and higher quality optical fibers, which take up less space, are expensive.
Optical fibers also lack mechanical properties necessary to be used with an interventional device. Optical fibers can break when flexed and have a relatively high stiffness compared to conventional catheter materials. Therefore, it is difficult to design a flexible tip for a catheter, which includes optical fibers and overall flexibility of an interventional device which include optical fibers is limited.
Furthermore, optical fibers require an expensive terminating connector and must be properly coupled to afford adequate light throughput. Signal efficiency of fiber based devices depends greatly upon the devices"" ability to couple sufficient light into the fibers at the desired wavelength. For spectral analysis, filtered broadband light sources are preferred over laser light sources for cost and frequency versatility. However, it is a challenge to efficiently couple light from a lamp source into fibers with small diameters. Although laser light is more easily coupled into optical fibers, laser light sources are generally more expensive, are obtainable in only a few selected wavelengths, and are subject to more critical regulatory controls than other light sources. Furthermore, light emitted by the subject illuminated by a laser light tends to be weak and is also subject to all of the loss mechanisms and inefficiencies problematical to a laser system.
Additional hardware, such as connectors and couplers, and the need to provide one or more optical conduits along the length of the interventional device, make conventional devices used for spectral analysis relatively expensive, inconvenient, and perhaps impractical.
In one aspect, the invention features a miniature spectrometer for use in spectral analysis. The spectrometer includes a light source and a light detector for placement inside a body such that optical conduits are not necessary to deliver light signals to and from tissue inside the body. The miniature spectrometer includes the light source and one or more light detectors. The light source illuminates a tissue region and the light detectors detect optical properties of the illuminated tissue by measuring modified light signals. The light detectors convert optical signals to electrical signals such that one or more electrical wires placed inside an interventional device can deliver the electrical signals from the tissue to a signal display or a microprocessor.
Embodiments of this aspect of the invention include the following features. The light source and the light detectors are energized by an external power supply through electrical wires. In another embodiment, an optically transparent tip encapsulates a spectrometer. The tip is shaped to optimize tissue contact and optical transmission. The tip encapsulating the spectrometer is disposed at a distal end of an interventional device. The tip may be coated with a material to improve light transmission. The tip may include at least one fluid channel, which is in communication with a lumen inside the interventional device, to deliver a fluid to a tissue region. In one disclosed embodiment, a spectrometer of the invention includes a light source and the light detectors formed on a single substrate. The light source may be a light emitting diode and the light detectors may be a photodiode comprising multiple channels, where both devices are formed on a silicon substrate. The light detector can include multiple channels to detect light emission at multiple wavelengths.
In another aspect, the invention features a method for characterizing tissue. According to the method, a spectrometer which includes a light source and a plurality of light detectors is provided. The spectrometer is placed inside a body near a tissue region to be characterized. The light source and the detectors are connected to a power source through electrical wires. The energized light source generates light and illuminates the tissue region. The detectors measure light signals modified as a result of interacting with the tissue region. The light detectors convert received optical signals to electrical signals. In one embodiment of this aspect of the invention, an optically transparent tip encapsulates the spectrometer and is located near a distal end of an interventional probe. The method can further include the step of rotating the spectrometer with respect to the tip. The rotation adjusts optical properties of the light transmitted to illuminate the tissue.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.